UNIT II.1 Unit Conversions

II.1 Unit Conversions You MUST learn and use the unit conversion method (not your own method!) A CONVERSION FACTOR: is a fractional expression relating or connecting two different units.

II.1 Unit Conversions Example 1: There are 60 seconds in 1 minute. In statement form, 1 min = 60 sec Conversion Factors: The conversion factor relates 2 units (minutes to seconds).

II.1 Unit Conversions Example 2: $1.44 per dozen eggs. Conversion Factors: Conversion factors do not change the VALUE of something, they just change the UNITS. To change the UNITS, multiply by the CONVERSION FACTOR.

II. 1 Unit Conversions THE UNIT CONVERSION METHOD: We need 3 important pieces of information: unknown amount and units initial amount and units conversion factor (relating the initial units to units of unknown)

II. 1 Unit Conversions Example 3: How many seconds are in 20 minutes?   Unknown amount: Initial amount: Conversion factor: Solution ** ALWAYS include UNITS in your calculations!

II.1 Unit Conversions Example 4: If a car can go 90km in 1 h, how far can the car go in 6.5 h? Unknown amount: Initial amount: Conversion factor: Solution

II.1 Unit Conversions Example 5: If the price of gas is $1.10 per liter (l), how much will it cost to fill a 40 liter tank? Unknown amount: Initial amount: Conversion factor: Solution

II.1 Unit Conversions HOW TO PUT EVERYTHING TOGETHER The general form of a unit conversion calculation is: (Unknown amount) = ( Initial amount) x (Conversion factor)

II.1 Unit Conversions Example 6 a. If 0.200 mL of gold has a mass of 3.86 g, what is the mass of 5.00 mL of gold? Unknown amount: Initial amount: Conversion factor:   Solution

II.1 Unit Conversions *Important: Always ask yourself “which way do I have to write the conversion factor so that my units cancel properly?” b. If 0.200 mL of gold has a mass of 3.86 g, what is the volume occupied by 100.0 g of gold?   Unknown amount: Initial amount: Conversion factor: Solution

II.1 Unit Conversions SUMMARY Identify unknown amount and its units (put on left side of = sign). Identify the initial amount and its units (put on right side of = sign). 3. Identify conversion factor. (Multiply initial amount by conversion factor in such a way that one of the units cancel. You want to be left with units of unknown amount!) 4. Complete the problem by multiplying and/or dividing amounts of RHS.

Assignment

II.1 Unit Conversions Multiple Unit Conversions We can solve problems that require more than one conversion factor. Example: If eggs are $1.44 per dozen, and if there are 12 eggs in a dozen, how many individual eggs can be bought for $4.32? ANALYZE THE PROBLEM: Unknown amount: Initial amount: Conversion factors:

II.1 Unit Conversions Solution: we require the connection conversion factor 1 gives the connection: conversion factor 2 gives the connection: Combining conversion factors 1 and 2 gives:

II.1 Unit Conversions Solve for unknown amount: Unknown amount = Initial amount x Conversion factors (1 and 2)

Assignment